1. Field of the Invention
The present invention relates to an apparatus for detecting the wheel positions of a vehicle, on which respective wheels are installed, an apparatus for detecting the inflation pressure of the tires of a vehicle, such as a direct-type tire inflation pressure detection apparatus, and transceivers therefor.
2. Description of the Related Art
A direct-type apparatus for detecting the inflation pressure of tires of a vehicle is known. This tire inflation pressure detecting apparatus is provided with a transceiver equipped with a sensor such as a pressure sensor, which is directly installed on each wheel with a tire. An antenna and a receiver are provided in the vehicle body. Thus, when the receiver receives, via the antenna, from the transmitter a detection signal detected by the sensor, the receiver is able to detect the inflation pressure of each tire based on the received detection signal.
In this direct-type tire inflation pressure detecting apparatus, it is determined whether or not data which has been received is coming from the transceiver of the own vehicle and it is determined on which of the wheels a transceiver in question is installed. For these determinations, as shown in U.S. Pat. No. 5,602,524 (which corresponds to Japanese Patent No. 3212311), data to be transmitted from each transceiver additionally contains ID (identification) information to distinguish the own vehicle from other vehicles and identify each wheel with the transceiver. The ID information is previously stored in the receiver and, when the receiver receives data from the transceiver, the stored ID information and the received ID information are used to determine the wheel the data is coming from.
Without the ID information assigned to each of the wheels, a received data cannot be determined as to which of the transceivers corresponding to the respective wheels the data is originated from. In other words, without using the ID information, the positions of the individual transceivers in the vehicle cannot be detected. Therefore, for example, when a user changes the positions of the tires by rotation, for example, the user has to read the ID information of the rotated tires and renew the ID information that has been registered up to then. Without doing this, the tire inflation pressure detecting apparatus cannot cope with the position change of the wheels.
Therefore, it is desired that a tire inflation pressure detecting apparatus can detect the wheels equipped with the respective transceivers without using the ID information (wheel-position information). In other words, it is desired that a tire inflation pressure detecting apparatus can detect the positions on which the respective transceivers are installed. Alternatively, where it is necessary to renew the ID information because of the position change of the wheels, the renewal of the ID data is desired to be automatically performed.
On the other hand, U.S. Publication No. 2004/95233 suggests an apparatus for specifying wheel positions. This apparatus includes an antenna for front wheels, which is located so that the distances therefrom to the left- and right-front wheels will be different, and an antenna for rear wheels, which is located so that the distances therefrom to the left- and right-rear wheels will be different. LF (low-frequency) waves are outputted from these antennas for transmission to transceivers (sensors) set at the individual wheels. The wheel positions are specified based on the reception rate of the LF waves at the individual transceivers. More specifically, the distances from the front-wheel antenna to the transceivers for the left- and right-front wheels are different, and the distances from the rear-wheel antenna to the transceivers for the left- and right-rear wheels are different. Further, the larger the distance is from the generation source of the LF waves to the destination, the weaker the intensity of the LF waves become. Accordingly, the reception rates of the LF waves are different between the transceivers installed on the left- and right-front wheels. Similarly, the reception rates of the LF waves are also different between the transceivers installed on the left- and right-rear wheels. Making use of this property, correlation of the transceivers to the left- and right-front wheels and to the left- and right-rear wheels is detected.
Further, U.S. Pat. No. 6,888,446 suggests an apparatus for detecting correlation of the individual transceivers to the respective wheels. In this apparatus, the detection is conducted making use of the fact that distances from various noise generation sources in the vehicle to the individual transceivers installed on the respective wheels are different, and also making use of the property that the larger the distance is from a noise generation source to a transceiver, the weaker the intensity of the noise becomes.
However, the apparatus disclosed in U.S. Publication No. 2004/95233 is required to establish a relationship that the LF waves outputted from the front-wheel antenna are reliably transmitted to one of the left- and right-front wheels and not to the other. The same applies to the LF waves outputted from the rear-wheel antenna. The establishment of these relationships depends on the intensities of the LF waves and the reception sensitivities of the individual transceivers. These relationships are very difficult to be established. Even if there is a design that can establish such relationships, the design may have poor flexibility. In addition, even if such relationships can be established, it will take time for calculating the reception rates of the LF waves at the transceivers for the left- and right-front wheels and the reception rates of the LF waves at the transceivers for the left- and right-rear wheels. Accordingly, the time taken for the wheel position detection will be long. This may also involve a difficulty, for example, of reliably detecting the wheel positions before traveling. In the case where tire inflation pressure is detected on the basis of the results of the wheel position detection, it is particularly important to provide a configuration which can reliably detect the tire inflation pressure before traveling.
The apparatus disclosed in U.S. Pat. No. 6,888,446 has poor compatibility with vehicles because the noise generation sources are different depending on the types of the vehicles. In other words, this apparatus has a difficulty in achieving good compatibility with vehicles regardless of the types of the vehicles. In particular, in the case where wheel position detection is carried out merely based on noises, the apparatus cannot cope with such noises that are produced by devices loaded on the vehicle according to the user's taste. Further, the timing of each of the noises that are considered to be produced during the on-state of the ignition switch cannot be estimated. Therefore, it is not easy to simultaneously transmit triggering signals to all of the transceivers for the purpose of wheel position detection. For this reason, it will take a long time to conduct the wheel position detection, or it will be difficult, for example, to reliably conduct wheel position detection before traveling.